Electron emission source composition for flat panel display and method of producing electron emission source for flat panel display using the same

ABSTRACT

Disclosed is an electron emission source composition for a flat panel display using the same, comprising carbon nanotubes, a vehicle, and an organotitanium or an organometallic compound, and a method of producing the electron emission source composition having improved adherent strength with the substrate and providing stable and uniform electron emitting characteristics.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electron emission source compositionand a method of producing an electron emission source for a flat paneldisplay using the same, and, more particularly, to an electron emissionsource composition having an improved adherent strength with thesubstrate as well as stable and uniform electron emittingcharacteristics, and a method of producing an electron emission sourcefor a flat panel display using the same.

2. Description of the Related Art

Earlier field emission displays (hereinafter referred to as “FED”) weremade of a spindt-type electron emission source including Mo or Si, withsharp tips of sub-micron size. Since the spindt-type electron emissionsource is assembled in a sub-micron size, the method of fabricating thesame requires a great deal of attention, and such an operation isconsidered high-level precision work. Thereby, it is difficult andexpensive to produce a large-sized field emission display device.

Carbon material has recently emerged as a potentially useful electronemission source due to its low work function. One carbon material, acarbon nanotube (CNT), is particularly anticipated to be an idealelectron emission source since it features a high aspect ratio and asmall tip radii of curvature of 100 Å, and thereby electrons are readilyemitted by applying an external voltage of as low as 1˜3 V/μm.

Generally, the electron emission source is fabricated in a such mannerthat the carbon nanotube is formed in a paste with a solvent, a resin,and so on, and it is applied between substrates by a screen-printingmethod, then it is sintered. Since the carbon nanotube has a low workfunction, the resultant electron emission source can be driven byapplying low voltages, and the method of fabricating the same is notcomplicated. It will thereby offer advantages to realize a large sizepanel display.

However, when the electron emission source is produced with carbonnanotubes by the screen-printing method, each carbon nanotube 1 isroughly mixed with a solid powder present in the paste, and the tips ofmost carbon nanotubes 1 are covered by the solid powder as shown in FIG.5. Consequently, the electron emission capabilities are not fullyutilized.

Therefore, there are considerable demands to find a way to expose thetips of the carbon nanotubes. As one scheme to satisfy such demands,Korean patent laid-open publication No. 2000-74609 discloses that carbonnanotubes are admixed to metal powders. However, this method requires anadditional process to expose and distribute the carbon nanotubes,rendering the process overly complicated.

Further, Japanese patent laid-open publication No. 2000-223004 disclosesa method for exposing the carbon nanotubes in which carbon and the metalparticulate are mixed and compacted, then the compacted mixture is cutand selectively etched. However, this method is also substantially toocomplicated and is difficult to be applied to a field emission device ofan electron emission array.

Moreover, Japanese patent laid-open publication No. 2000-36243 disclosesa method in which a laser beam is irradiated on the surface of a printedpattern in which carbon nanotubes are covered with silver particlescombined with a binder, and the silver particles and the binder presenton the surface are selectively removed, so that the carbon nanotubes areexposed. However, the method has a concern in that the carbon nanotubesget thermally damaged by the laser irradiation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electron emissionsource composition capable of increasing the adherent strength onto thecathode and providing stable and uniform electron emissioncharacteristics.

It is another object to provide a method of producing an electronemission source for a flat panel display using the above-mentionedcomposition.

It is still another object to provide a flat panel display using theabove-mentioned composition.

These and other objects may be achieved, according to an embodiment ofthe present invention, by an electron emission source compositionincluding carbon nanotubes, a vehicle, and an organotitanium or anorganometallic compound.

In order to achieve these objects and others, the present inventionfurther provides a method of producing an electron emission source for aflat panel display including mixing carbon nanotubes, a vehicle, and anorganotitanium, or an organometallic compound, to provide a carbonnanotube composition; screen-printing the carbon nanotube compositiononto a substrate; and sintering the resultant substrate.

The present invention further provides a flat panel display including asubstrate, an electrode formed on the substrate and an electron emissionsource layer formed on the electrode, the layer having micro-cracks ofat or between 0.1 and 100 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention, and many of the attendantadvantages thereof, will be readily apparent as the same becomes betterunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view showing a substrate in whichan electrode is coated with the electron emission source compositionaccording to an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view showing a substrate in whichmicro-cracks are formed on the surface of a carbon nanotube layeraccording to an embodiment of the present invention;

FIG. 3 is a scanning electron microscope (SEM) photograph showing thesurface of an electron emission source according to Example 1 of anembodiment of the present invention;

FIG. 4 is a 100-fold enlarged SEM photograph of the SEM photograph ofFIG. 3; and

FIG. 5 is a schematic view showing a conventional electron emissionsource.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an electron emission source compositionincluding carbon nanotubes as an electron emission source of a filedemission device. The composition includes a vehicle and anorganotitanium, or an organometallic compound, in addition to the carbonnanotubes.

The contents of organotitanium or the organometallic compound arepreferably 20 to 95 wt %, and more preferably 40 to 95 wt %. In a casewhen the content of the organotitanium or the organometallic compound isless than 20 wt %, it is hard to make micro-cracks on the carbonnanotube layer; whereas, when the content is more than 95 wt %, therelative amount of the electron emission source is overly decreased andtoo many cracks are generated for the carbon nanotube layer to adhere toand to be printed on the substrate. The represented examples oforganometallic compounds available in the present invention include, butare not limited to, any organometallic compound including metalsbelonging to 3, 4, 5, and 6 groups of the Periodic tables. These includeTi, Si, B, Ta, Nb, Zr, Sn, Sr, Al, or In, specifically, Si(O-n-C₄H₉)₄,Al(iC₄H₉)₃, and Ti(O-n-C₃H₇)₄. However, it is understood that anymaterial capable of generating micro-cracks during the sintering processcan be included without departing from the scope of the disclosedinvention.

The term carbon nanotube means any material generated from the chemicalpotential difference between a catalyst and a carbon material, which isinduced from a thermal decomposition process, the material also having atube-like or cylinder-like shape and having a diameter of about 1 to 10nanometers. Nanotubes may be classified into a single wall nanotube, amulti-wall nano-tube, and a coil nanotube, according to the coiled formthereof. The electron emission source composition according to thepresent invention includes carbon nanotubes of 5 to 80 wt % based on thetotal weight of the composition, and more preferably 5 to 60 wt %. Thecontent is determined by considering the amounts of the organotitanium,or the organometallic compound, and the vehicle.

The vehicle is intended to improve the printability, so it has a role toadjust viscosity, concentration, and so on. It may include anyconventional material capable of being used in a paste composition. Thevehicle includes a thickener, a binder, and a solvent. The thickener isused to enhance the adherent strength between layers, and it includes asilicone-based material and a mineral oil such as terpineol. Further,the binder includes an organic resin such as ethyl cellulose, acrylresin, epoxy resin, and so on. The solvent includes butyl carbitolacetate, terpineol, ethyl cellulose, ethyl carbitol, or any organicsolvent such as animal oil and vegetable oil.

As the vehicle is for facilitating the printing of the pastecomposition, it will be completely removed by evaporation duringsintering of the printed substrate. The amount of the vehicle used willbe adjusted depending on the amounts of main components such as carbonnanotubes and organotitanium, or an organometallic compound, in theelectron emission source composition.

In an embodiment of the present invention, with reference to FIGS. 1 and2, the method of producing the electron emission source commences withthe step of adding organotitanium, or an organometallic compound, to amixture of carbon nanotubes 1 and the vehicle, to provide an electronemission source composition layer 4.

The resultant electron emission source composition is applied to thecathode 2 formed on the substrate 3 by the screen-printing method, toform an electron emission source composition layer 4 on the cathode 2(FIG. 1). Subsequently, the substrate 3 printed with the electronemission source composition layer 4 is sintered at or between 250 and600° C. The sintering temperature is determined in an appropriate rangeby considering the complete combustion temperature of the organometalliccompound and the oxidation temperature of the carbon nanotubes 1. Duringthe sintering process, the vehicle is completely removed by evaporation,and micro-cracks 5 of at or between 0.1 and 100 μm are generated on thesurface of the electron emission source composition layer 4 due to thepresence of the organotitanium, or the organometallic compound, so thatthe carbon nanotubes 1 are exposed (FIG; 2).

Consequently, the carbon nanotubes 1 of the present invention canprovide stable and uniform electron-emitting characteristics. Further,by using the organotitanium, or the organometallic compound, as abinder, the carbon nanotubes 1 are easily adherent to the cathode 2, andthe micro-cracks 5 are presented on the surface of the electron emissionsource composition layer 4. Thereby, the carbon nano-tubes 1 are exposedthrough the micro-cracks 5 so that it is possible to provide stable anduniform electron emitting characteristics.

The following examples illustrate embodiments of the present inventionin further detail. However, it is understood that the present inventionis not limited by these examples.

EXAMPLE 1

In this example, 40 wt % of carbon nanotubes 1 was mixed with 20 wt % ofa terpineol solvent. To this mixture, 40 wt % of an organometalliccompound Ti(O-n-C₃H₇)₄ was added to obtain an electron emission sourcecomposition 4.

The obtained electron emission source composition 4 was applied to thecathode 2 formed on the substrate 3 by the screen-printing method, andit was sintered at 400° C. for 30 minutes.

FIG. 3 shows a SEM photograph of the surface of the resultant electronemission source 4 fabricated by the method according to Example 1, andFIG. 4 shows the SEM photograph magnified 100-fold from that of FIG. 3.A carbon nanotube is represented as 1, a cathode is 2, and a substrateis 3 in FIGS. 3 and 4. As shown in FIGS. 3 and 4, it is recognized thatthe carbon nanotubes 1 are exposed through the micro-cracks 5 on thesurface of the electron emission source composition layer 4 according toan embodiment of the present invention.

The electron emission source composition 4 of the present invention isprepared by adding the organotitanium, or the organometallic compound,to the carbon nanotubes 1 so that micro-cracks 5 are generated on theresultant electron emission source composition layer 4 during thesintering step. It is thereby possible for the carbon nanotubes 1 toincrease the-adherent strength relative to the substrate 3, as well asto provide stable and uniform electron emitting characteristics.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1-9. (canceled)
 10. A method of producing an electron emission sourcefor a flat panel display comprising: providing a carbon nanotubecomposition comprising carbon nanotubes, a vehicle, and an additive ofan organotitanium compound or an organometallic compound;screen-printing the carbon nanotube composition onto a substrate; andsintering the resultant substrate.
 11. The method according to claim 10,wherein the carbon nanotubes are present in a range of about 5 wt % toabout a 80 wt %, and the organotitanium compound or the organometalliccompound is present in a range of about 20 wt % to about 95 wt %. 12.The method according to claim 11, wherein the carbon nanotubes arepresent in a range of about 5 wt % to about a 60 wt %, and theorganotitanium compound or the organometallic compound is present in arange of about 40 wt % to about 95 wt %.
 13. The method according toclaim 10, wherein the sintering step is performed at a temperature in arange of about 250° C. to about 600° C.
 14. The method according toclaim 10, wherein the organometallic compound comprises a metal selectedfrom the group consisting of group 3 of the Periodic Table, group 4 ofthe Periodic Table, group 5 of the Periodic Table, and group 6 of thePeriodic Table.
 15. The composition method according to claim 10,wherein the organometallic compound is selected from the groupconsisting of Ti, Si, B, Ta, Nb, Zr, Sn, Al and In.
 16. The methodaccording to claim 10, wherein the organometallic compound is selectedfrom the group consisting of Si(O-n-C₄H₉)₄, Al(iC₄H₉)₃, andTi(O-n-C₃H₇)₄.
 17. The method according to claim 10, wherein the vehiclecomprises a binder and a solvent.
 18. The method according to claim 17,wherein the binder comprises an organic resin.
 19. The method ofaccording to claim 17, wherein the solvent comprises a compound selectedfrom the group consisting of butyl carbitol acetate, terpineol, ethylcellulose, ethyl carbitol, animal oil and vegetable oil.
 20. A flatpanel comprising: a substrate; an electrode formed on the substrate; andan electron emission source layer formed on the electrode, the layerhaving micro-cracks in a range of about 0.1 μm to about and 100 μm.